FIG. 1 illustrates a source driver used in an LCD (Liquid Crystal Display) device. The source driver 100 shown in FIG. 1 comprises a shift register 102, a line buffer 104, a level shifter 106 and a digital-to-analog converter (DAC) 108. The line buffer 104 stores and outputs digital data signals by the control of the shift register 102. The level shifter 106 shifts voltage levels of the digital data signals. The digital-to-analog converter (DAC) 108 generates a driving voltage Vd to drive the LCD according to the outputted signals from the level shifter 106.
FIG. 2 illustrates a conventional level shifter. As shown in FIG. 2, the level shifter 106 comprises a first transistor 202, a second transistor 204, a third transistor 206, a fourth transistor 208, and a fifth transistor 210. The level shifter 106 receives the high voltage source VDDA via the transistor 210, receives input voltages via the input nodes IN1 and IN2 for outputting via output nodes OUT and OUTB.
To speed up and save power, the voltage source of ICs tends to decrease, for example from 3.3V to 2.5V and further to 1.8V. However, the transition of the level shifter would become slower since the voltage level of the input signal is decreased such that the response time of the transistors of the level shifter is increased.